Effect of prolonged and neonatal capsaicin treatments on the substance P immunoreactive nerves in the rabbit eye and spinal cord.

Substance-P (SP) immunoreactivity was demonstrated in the rabbit eye and spinal cord using monoclonal SP antibody and an indirect immunofluorescence technique. Norves containing SP immunoreactive material were found in the cornea, iris and ciliary body of which the iridic sphincter had the densest innervation. Neither prolonged subcutaneous treatment (up to 280 mg/kg) augmented by intracameral capsaicin injection nor neonatal treatment with drug 70 mg/kg eliminated this immunoreactivity, though both blocked the miotic effect of intracameral SP. It is concluded that capsaicin is not specific SP depleting agent but rather a neurotocic substance that affects noxious pathways and probably prevents the release of the SP retained by the nerve following the treatment used.